Exo-3-furanylidenes and 3-pyranylidenes products having cis-2,5
and cis-2,6 substitution were synthesized from terminally substituted
alkynyl alcohols with various aldehydes via Prins-type cyclization and trapping
of the resulting vinyl cations as vinyl triflates in good yields. Vinyl
triflates underwent a subsequent stereoselective hydrolysis to give the
corresponding 3-acyl-substituted products.